1. Field of the Invention
The invention relates to a filling body with channels for the flow of liquid and gas mixture, and which may be applied especially for units in sewage treatment plants, as submerged biological units, active units with bound biological skin dripping bodies filling bodies of cooling-towers, etc.
2. Description of the Related Art
It is known that one of the state of the art methods for purification of organically polluted sewage effluent is applying active units with a bound biological skin (biofilm). Anaerobic and aerobic techniques are identified.
In both cases a skin developed from micro-organisms is bound to the surface of immersible units submerged under a working water line. This skin is the active agent of the system. The immersible unit consists of elements of high specific surface, as of mesh, screen, strainer, porous material, or a vertically coursed medium (e.g. by upright channels).
The biological skin formed on the surface of the immersible unit--for an aerobic system--is to be supplied with oxygen. Blowing air or technical oxygen into the water under the immersible unit is how the need is satisfied. The bubbles of the effluvium move upward within the courses of the immersible unit and tortuous flow develop around them locally. Consequently, the dissolution of the gas becomes more efficient, a solution of higher oxygen-concentration flows through the channels, and the speed of flow increases.
All these result in a more efficient gas-exchange between the moving liquid and the biofilm, and in a more efficient operation of the system. That type of aerobic system is called a system of contact-oxidation with bound biofilm.
Other techniques for the biological treatment of sewage are also known, as piping the effluent into treating lagoons, oxidation ponds, or systems working with a double sort of activated sludge, which later utilize the impact of both the surface bound and floating micro-organisms. The surface bound skin is settled to the skirts of contact devices.
A contact device is a unit assembled into a system, or adequate for being assembled into a system called generally a filling body.
There are several requirements a filling body must satisfy. It must have a large specific surface, be sufficient to consolidate the biological skin, and be fitted with channels serving the course and turbulent flow of the liquid. The cross sectional area of the channels is most suitable if the bubbles moving up result in a speedy flow of the effluent. Additionally the local differences in the concentration of the chemical constituents issue a rapid and effective material exchange between the liquid and the channel's surface due to a turbulent flow. In an aerobic system, the increased degree of the gas exchange between the liquid and the bubbles is an added result of the turbulent flow. The active surface of the filling body related to its volume (described by a measure like m.sup.2 /m.sup.3) represents another meaningful nature of the filling body. With the increase of this measure, the total area of the biofilm might be increased, thus the enlargement of this character is also an important requirement. However, the decrease of the cross sectional area of the channels is curbed by the undesirable declination of the velocity of the flowing liquid, or liquid/gas mixture.
It is requested, further, that the material of the filling body shall be chemically resistant, lightweight, helpful in consolidating the biofilm to its surface, and inexpensive. The production of the units and the assembly of the filling body shall be simple. For the most part these requirements are satisfied by using units and filling bodies of plastic, synthetic, or other compound material.
There are many known types of filling bodies and contact units made of compound material, however these satisfy the listed requirements only partly.
German patent specification no. 2901509 describes a zigzagged contact unit. The inconvenience of this type of unit is that the air-lift effect of the gas-bubbles (compare w/the mammoth pump) is discounted due to the considerable hydraulic headloss of the disperse matter migrating through the contact unit. In addition, supplementary impact-energy has to be applied to develop a turbulent flow.
An existing type of the contact unit is having vertical channels of circular cross sectional shape (pipes). The outer skirt of the pipes is fallow and the useful area utilized for consolidating the biofilm is only 40 to 60% of the total area.